1. Field of the Invention
The present invention relates to a centrifugal compressor which is required to provide high efficiency and a wide operational range.
2. Description of the Prior Art
Some centrifugal compressors include a plurality of stator blades arranged at equal intervals about a circumference of the diffuser disposed around the impeller. The spaces between the stator blades and the space between the side walls of the diffuser cooperate to provide a diffuser passage. In an operational region where the rotational speed is high and the flow rate is low, a separation area is generated on the negative-pressure surfaces of the stator blades, thereby failing to achieve a sufficient increase in pressure. This first results in the so-called rotating stall, in which the separation area rotates in the circumferential direction. When the flow rate is further decreased, a surging phenomenon occurs. One form of the art for shifting the surging phenomenon to a low flow-rate side comprises a proposal of a centrifugal compressor in which auxiliary blades are arranged radially inwardly of the spaces between stator blades arranged at equal intervals on the diffuser and in which stator or auxiliary blades have leading edges inclined in the downstream direction while extending away from the side plate toward the core plate (e.g., Japanese Patent Unexamined Publication No. 1-247798).
However, such a centrifugal compressor, in which leading edges of stator or auxiliary blades are inclined in the downstream direction while extending away from the side plate toward the core plate, does not sufficiently prevent a surging phenomenon in a low flow rate region. Further, since the compressor has stator blades are arranged at equal intervals throughout the circumference of the diffuser disposed around the impeller, sufficient consideration has not been paid to the prevention of rotating stall.